Vapor recovery method and system



Aug. 16, 1966 E. L. MORAGNE VAPOR RECOVERY METHOD AND SYSTEM Filed Jan. 14, 1965 Edward L Moray/7e INVENTOR.

ATTORNEY United States Patent 3,266,262 VAPOR RECOVERY METHOD AND SYSTEM Edward L. Moragne, 4723 Nenana Drive, Houston, Tex. Filed Jan. 14, 1965, Ser. No. 425,481 14 Claims. (Cl. 62--.54)

This invention relates to a method and system for the recovery of liquefiable components of hydrocarbon vapors, and more particularly to the recovery of gasoline components from vapors expelled from tanks during the filling thereof.

In the loading of truck tanks, tank oars, ship tanks and the like with volatile hydrocarbon liquids, particularly gasoline, substantial quantities of the lighter components will vaporize and will be lost to the atmosphere unless suitable recovery methods or systems are employed. The quantities so lost may prove quite substantial, being dependent upon the vapor pressure of the initial liquid and the temperatures at which the filling of tanks occurs. In addition to the economic loss occasioned by the loss of valuable hydrocarbon components, the vapor loss may also create a serious fire hazard by reason of the flammable character of the vapors.

The methods hereto before employed generally require rather complicated suction pumps and compressors for conveying the vapors escaping from the tanks to suitable condensation and fractionation equipment and are generally comparatively inefficient, unless highly expensive and rather extensive apparatus systems are employed.

The present invention has for its primary object the provision of an improved recovery system which is highly efficient in effecting condensation and recovery of maximum quantities of the liquefiable hydrocarbons.

An important object is the provision of a method of recovery which obviates the need for pumps or compressors for collecting and delivering the vapors to the recovery apparatus.

A furtther object is the provision of a method which employs multiple-stage cooling to effect condensation of the condensable hydrocarbon components.

Another object is the provision of a method employing two stages of cooling of the vapors to successively lower temperatures, the vapors being cooled in the first stage to a temperature just above the freezing point of water in the range from about 33 F. to about 35 F. to initially condense the major proportion of any water vapor present in the vapors to thereby obviate the formation of solid hydrates in the subsequent stage; and the vapors being cooled in the second stage to a temperature in the range from about 20 F. to about 30 F. sufiicient to condense the major proportion of the condensable hydrocarbon components of the vapors.

Yet another object is the provision of a method wherein movement of the vapors from the tank being filled is effected by the combination of displacement by liquid entering the tank and reduction in pressure occasioned by reduction in temperature and condensation in the liquid recovery steps of the method.

An additional object is the provision of a simple, highly compact and relatively inexpensive apparatus for carrying out the method in accordance with this invention.

Other and more specific objects and advantages of this invention will become more readily apparent from the following detailed description when read in conjunction with the accompanying drawing, which is a flow diagram illustrative of the appartus employed and illustrating the flow of materials through the system in accordance with the method of this invention.

Referring to the drawing, there is shown a loading rack R, of any known and generally conventional form,

3,266,262 Patented August 16, 1966 employed for loading truck tanks T with gasoline or other volatile hydrocarbon liquids passing through a meter M to loading lines L. The entrance of liquids into tank T will displace air normally present in such tanks and vapors normally evolving from the liquid, such as gasoline. The displaced vapors will be forced through pipe P to a header H from which the vapors, usually containing Water vapors present in the air initially in the tank, will flow through a line 10 to a conventional flash arrestor 11, and thence through a line 12 into a pre-cooler or heat exchanger 13 where the entering vapors will exchange heat wit-h a lower temperature stream of fixed gases flowing through a coil 14 disposed in exchanger 13. The character of the fixed gases and their source will be described more fully hereinafter. The vapors initially cooled by the fluid flowing through coil 14 will then enter a vertically disposed column 15, herein termed the liquefier, and will flow upwardly successively through first and second coil-type chillers 16 and 17, respectively, wherein the upflowing vapors will be chilled to successively lower temperatures by a suitable refrigerant fiowing through the coils of the respective chillers. As illustrated the shell of heat exchanger 13 may be on the side of column 15 to be in open communication therewith. The uncondensed, generally inert gases leaving chillers 16 and 17 will flow out of the upper end of column 15 through a line 20 which leads to the inlet of pre-cooler coil 14, from which the gases will flow through a line 21 to the atmosphere.

A generally conventional refrigeration system is employed to produce the necessary chilling temperatures in chillers 16 and 17 and comprises a refrigerant compressor 25 having a suction pipe 26 and a discharge pipe 27 leading into a condenser 28 wherein a suitable and generally conventional refrigerant is liquefied and discharged through a pipe 29 into a receiver 30. A line 31 is connected to the receiver for the delivery of liquefied refrigerant into a header 32 in which are mounted expansion valves 33 and 34 for expanding portions of the refrigerant, respectively, into chillers 16 and 17. A refrigerant return line 35 having a back-pressure valve 36 therein, is connected to the second stage chiller 17 and leads back to suction line 26 going to the refrigerant compressor, thereby completing the refrigerant cycle.

Column 15 is provided with a sump or Well 37 fitted with a liquid level controller 38 which is operably connected to a discharge valve 39 mounted in a line 40 lead ing from the bottom of well 37. The lower portion of column 15 above well 37 is equipped with a second liquid level controller 41 operably connected to a control valve 42 mounted in a discharge pipe 43 leading from a point in the bottom of column 15 just above well 37. Pipe 43 is connected to a pump 44 which is controlled by a conventional electrical controller 45 operated by liquid level controller 41. Pump 44 is connected to a discharge line 46 having a valve 47 mounted therein.

Operation of the method and apparatus is as follows: As noted previously and as indicated on the flow diagram, vapors, which include air usually containing some water vapor initially present in the truck tank, together with light hydrocarbons vaporized from the gasoline as it is delivered into the truck tank, will be displaced therefrom into pipe P by the liquid entering the tank, as the filler opening of which will usually be sealed about the filler and vapor outlet pipes. The displaced vapors Will be forced through pipe P and header H into vapor line 10 leading to the recovery system. The displacement of the vapors by the liquid in the truck tank will be assisted by the reduction in pressure occasioned by the reduction in temperature and resulting condensation which takes place in the recovery system to move the vapors to the latter,-

thereby eliminating the need for a gas compressor or the like, for pumping the vapors to the recovery system.

The vapors will pass through flash arrestor 11 and thence through the shell of exchanger 13 into the vertically disposed liquefier column 15. The vapors entering the column will be pre-cooled by heat-exchange in exchanger 13 with the cold fixed or inert gases passing out of the top of column 15 through pipe 20 and thence through coil 14 to discharge pipe 21. The entering vapors passing through heat exchanger 13 will thus be partially cooled, generally to a temperature about F. below the ambient atmospheric temperature, and will flow therefrom into column 15 and thence upwardly successively through first stage chiller 16 and second stage chiller 17 wherein the vapors will be cooled to successively lower temperatures sufficient to effect the desired degree of condensation of the liquefiable components. The vapors denuded of the liquefiable components will then flow out of column 15 through pipe 20, as previously noted.

First stage chiller 16 will be maintained at a temperature such as to chill the vapors to a suitable dew point temperature for the water vapor present in the vapors. This temperature will ordinarily be in the range of from about 33 F. to 35 F., being carefully maintained to be just above the freezing point of water. As a result of this first stage cooling, substantially all of the water vapor will be condensed and will separate from the uncondensed vapors and will fall to the bottom of column 15, collecting in well 37 to form the body W from which it will be continuously drained from the system through pipe 40 under control of liquid level controller 38. Some of the heavier hydrocarbon components will also condense at the temperature maintained in chiller 16.

The remaining hydrocarbon vapors and air thus freed of water vapor will then pass through second stage chiller 17 which will be maintained at a somewhat lower temperature than that in the first stage but sufficiently low to effect substantially complete condensation of the liquefiable hydrocarbons remaining in the vapors. This temperature will be in the range from about F. to about F.

By this sequence of fractional chilling steps, whereby the water vapor will be condensed at temperatures above the freezing point of water and removed from the vapors, hydrate formation will be substantially completely obviated, as might otherwise occur under the sub-freezing temperatures employed in the second stage chiller. Therefore, the mechanical difficulties frequently occasioned by the formation of hydrates will be eliminated.

The hydrocarbon components condensed in the precooler and the two chilling stages will separate from the fixed or uncondensed gases and will fall to the bottom of column 15 where they will form a layer G on top of the water collected in well 37. The liquefied hydrocarbons will be continuously withdrawn from column 15 by means of pump 44 under the control of liquid level controller 41 and discharged through pipe 46 to storage.

The multiple-stage cooling including the pre-cooling stage and the two-stage chilling heretofore described, has been found to be highly effective in recovering a very large proportion of the liquefiable components of the vapors. It is found, however, that the recovery may be additionally increased by passing the vapors in advance of each of the chilling stages through a bed of porous solid materials indicated at 18 and 19, and located in advance of chillers 16 and 17, respectively. These porous solids appear to act as agglomerating agents and their mechanism is not fully understood. The materials may be conventional alumina-silica catalysts commonly employed in many petroleum cracking and other refining process, or may be conventional alumina pellets impregnated with zinc oxide, the proportions of which may be varied in the respective catalyst beds, the proportion of zinc oxide to alumina in the second stage bed 19 being generally greater than in the first stage bed 18. As

indicated, no mechanism can be ascribed to the actions which occur by reason of contact of the vapors with these beds, but it has been found that the degree of condensation of liquefiable components is increased when these beds are employed over operations where the beds are eliminated, but the temperature conditions are otherwise the same.

It will be understood that the method and apparatus in accordance with this invention is designed primarily for use when the ambient atmospheric temperatures during loading of the gasoline or other volatile liquid are comparatively high, as under summer conditions, since it will be obvious that under low temperature winter conditions, the volatilization losses will generally be quite low, and sufficiently so that operation of the method and apparatus become unnecessary.

By means of the method and apparatus in accordance with this invention, it has been found that as much as 75% to of all of the liquefiable components in the vapors may be condensed and recovered, with resulting substantial saving in money values. In addition a vent gas stream is produced which is substantially denuded of flammable hydrocarbons and is substantially inert, being composed largely of the air originally present in the tank, with the result that its flammability and potential hazard is greatly reduced.

The apparatus heretofore described may readily be made very compact and has been constructed to be incorporated in a self-contained unit mounted on a skid, or other mobile platform which can be moved easily from place to place. Such a unit, for example, made about 11 feet in height, 8 feet in length, and 4 feet in width will house an apparatus assembly which is capable of handling about 3500 cubic feet of vapors per minute. A portable unit of even smaller size for connection to ship tanks during loading thereof and having a capacity of about 400 cubic feet per minute has been constructed.

It will be understood that various changes and modifications may be made in the details of the procedure and the apparatus within the scope of the appended claims but without departing from the spirit of this invention.

What I claim and desire to secure by Letters Patent is:

1. The method of recovering liquefiable components from vapors evolved during the filling of tanks with volatile hydrocarbon liquids, comprising, cooling the vapors in a first chilling stage to a dew point temperature for water vapor present in the vapors etfective to condense and separate the Water from the vapors, thereafter cooling the water-freed vapors in a second chilling stage to a lower temperature effective to condense and separate therefrom the condensable hydrocarbon components remaining in the vapors, and recovering the condensed hydrocarbons.

2. The method according to claim 1 wherein the temperature in the first chilling stage is in the range from about 33 F. to about 35 F.

3. The method according to claim 1 wherein the temperature in the second chilling stage is in the range from about 20 F. to about 30 F.

4. The method according to claim 1 wherein the temperature in the first chilling stage is in the range from about 33 F. to about 35 F. and in the second chilling stage in the range from about 20 F. to about 30 F.

5. The method of recovering liquefiable components from vapors evolved during the filling of a tank with volatile hydrocarbon liquids, comprising, transferring the evolved vapors to a liquefying zone, pre-cooling said vapors entering the liquefying zone, cooling the precooled vapors in the liquefying zone in a first chilling stage to a dew point temperature for water vapor present in the vapors effective to condense the major proportion of the water vapor, thereafter cooling the water-freed vapors in a second chilling stage to a lower temperature effective to condense the condensable hydrocarbon components remaining in said vapors, separately withdrawing water and the condensed hydrocarbons from the liquefying zone, discharging the finally uncondensed vapors from said zone, and passing said uncondensed vapors into heatexchange relationship with said vapors entering the liquefying zone to effect said pre-cooling.

6. The method according to claim 5 wherein the transfer of said evolved vapors is effected by liquid displacement thereof from the tank as the latter is being filled by said liquids.

7. The method according to claim 5 wherein the temperature in the first chilling stage is in the range from about 33 F. to about 35 F.; in the second chilling stage in the range from about 20 F. to about 30 F and wherein the temperature reduction attained by said pre-cooling is about F. below the ambient atmospheric temperature.

8. The method of recovering liquefiable components from vapors evolved during the filling of tanks with volatile hydrocarbon liquids, comprising, cooling the vapors in a first chilling stage to a dew point temperature for water vapor present in the vapors effective to condense and separate the water from the vapors, thereafter cooling the water-freed vapors in a second chilling stage to a lower temperature effective to condense and separate therefrom the condensable hydrocarbon components remaining in the vapors, passing said vapors in advance of each of said cooling stages through a body of a porous solid material selected from the class consisting of alumina-silica particles and alumina particles impregnated With ZnO and recovering the condensed hydrocarbons.

9. The method according to claim 8 wherein the proportions of ZnO in the respective beds are. increased in the direction of flow of said vapors through the chilling stages.

10. Apparatus for recovering liquefiable components from vapors evolved during the filling of a tank with volatile hydrocarbon liquids, comprising, a vertically disposed liquefier column, conduit means for delivering vapors from a tank in which they are evolved to an intermediate portion of said column, first and second vertically spaced chilling coils disposed in said column in the path of upward flow of the vapors through the column, means for circulating a refrigerant through said coils including means for controlling the chilling temperatures in the respective coils, means for withdrawing water from the lower end of said column, means for withdrawing liquefied hydrocarbons from an intermediate portion of the column, and a vent conduit communicating with the upper end of said column for discharging uncondensed vapors therefrom.

11. An apparatus according to claim 10 including a body of porous particulate solid material disposed in advance of each of said chilling coils in the path of flow of said vapors therethrough.

12. An apparatus according to claim 10 including vapor precooling means, comprising a closed coil connected to said vent conduit and disposed in said conduit means in the path of flow of the entering vapors.

13. Apparatus for recovering liquefiable components from vapors evolved during the filling of a tank with volatile hydrocarbon liquids, comprising, a vertically disposed liqucfier column, conduit means for delivering vapors from a tank in which they are evolved to an intermediate portion of said column, first and second vertically spaced chilling coils disposed in said column above the point of entry of said conduit means in the path of upward flow of the vapors through the column, means for circulating a refrigerant through said coils including means for controlling the chilling temperatures in the respective coils, a water-accumulating Well at the lower end of said column, a drain conduit communicating with said well, a first liquid level controller operatively connected to said well and to said drain conduit for controlling the water level in said well, a second conduit connected to the lower portion of said column above said well, a second liquid level controller operatively connected to the lower portion of said column above said well and to said second conduit to control the level of liquefied hydrocarbons accumulating in the column on top of said water level, and a vent conduit communicating with the upper end of said column for discharging uncondensed vapors therefrom.

14. An apparatus according to claim 13 including a body of a porous solid particulate material disposed in advance of each of said chilling coils in the path of flow of the vapors therethrough.

References Cited by the Examiner UNITED STATES PATENTS 2,346,253 4/ 1944 De Molte 62-54 2,379,215 6/1945 Brinkmann 6254 2,938,360 5/ 1960 Christensen 62-54 3,024,617 3/1962 Miller 6254 LLOYD L. KING, Primary Examiner. 

1. THE METHOD OF RECOVERING LIQUEFIABLE COMPONENTS FROM VAPORS EVOLVED DURING THE FILLING OF TANKS WITH VOLATILE HYDROCARBON LIQUIDS, COMPRISING, COOLING THE VAPORS IN A FIRST CHILLING STAGE TO A DEW POINT TEMPERATURE FOR WATER VAPOR PRESENT IN THE VAPORS EFFECTIVE TO CONDENSE AND SEPARATE THE WATER FROM THE VAPORS, THEREAFTER COOLING THE WATER-FREED VAPORS IN A SECOND CHILLING STAGE TO A LOWER TEMPERATURE EFFECTIVE TO CONDENSE AND SEPARATE THEREFROM THE CONDENSABLE HYDROCARBON COMPONENTS REMAINING IN THE VAPORS, AND RECOVERING THE CONDENSED HYDROCARBONS. 